Freezer storage bag

ABSTRACT

A recloseable multibag freezer bag including an inner liner bag and an outer support bag. The inner liner bag is a thermoplastic with a thickness of less than 2 mil and a specified secant modulus, has a mouth through which the interior of the inner liner bag is accessible, and is joined by a mouth seal to the throat of the support bag along the entire length of the mouth of the liner bag substantially enclosing an air space between facing walls of the inner liner bag and outer support bag. The outer support bag is a thermoplastic, and has a mouth and a throat. A recloseable mouth seal is affixed to its mouth to provide recloseable access to the interior of the liner bag through the outer bag while maintaining the enclosed air space between the inner and outer bags.

BACKGROUND

This invention primarily concerns the packaging of food, particularlymeat but is applicable to packaging other articles or items. Theinvention was made during attempts to make improved “freezer bags” forrepackaging and freezer storing uncooked red meat by the “consumer” in amanner that reduces so called “freezer burn”. However, various aspectsof the invention also apply to the “commercial” packaging or repackagingof food, such as by a supermarket or by butchers at a slaughterhouse.Other aspects of the invention include methods for preparing theimproved freezer bags; methods for using the bags; the packages of meat;and certain types of thermoplastic film being particularly suitable foruse as meat-contacting packaging material.

Reclosable Plastic Storage bags are extremely old in the art. Today,plastic bags are typically available to the public in cartons identifiedfor specific recommended “end use” (such as Storage Bags, Heavy DutyFreezer Bags, Vegetable Bags, Trash Bags). Often the bag itself islabeled by “end use”, for example, “ZIPLOC® BRAND Heavy Duty FreezerBags”.

The term “Freezer Bag” is hereby defined as a bag having significantfunctional utility in the storage of food in a freezer. “Freezer Bags”are typically available in the following sizes: 2 gallon (7.6 L); 1 (3.8L) gallon; pleated ½ gallon (1.9 L); quart (0.9 L); and pint (0.5 L).

The term “Freezer Burn” is hereby defined as the name for thedehydration that occurs when unpackaged or improperly packaged food isstored in the low humidity atmosphere of a freezer (see “Packaging FoodsWith Plastics”, by Wilmer A. Jenkins and James P. Harrington, publishedin 1991 by Technomic Publishing Co., Inc., at page 305).

Freezer burn has remained a major complaint among consumers despite thecommercial success of thick plastic freezer bags. In the short-term,freezer burn can be a reversible process. In the long-term, however,freezer burn causes a complex deterioration of food quality involvingundesirable texture changes followed by chemical changes such asdegradation of pigments and oxidative rancidity of lipids. Taste, aroma,mouth feel and color can all be ruined. Freezer burn of raw red meat isparticularly critical because of its impact upon the color of the meat.

Aforementioned “Packaging Foods With Plastics” provides an excellentstate of the art summary, with all the information on (commercial)“packaging fresh red meat collected in Chapter Seven”. Curiously, thebook does not appear to mention freezer burn, apart from defining it inthe glossary.

“Keeping Food Fresh” is the title of an article in “Consumer Reports”,for March, 1994, at pages 143-147. The article is too recent to beavailable as prior art to the extent that this application designatesthe United States. Nevertheless its contents are of interest in showingthe absence of certain types of prior art, and therefore enhancing thepatentability of the present invention.

The “Consumer Reports” article attempts to answer the question as towhich packaging material (plastic, aluminum, waxed paper, bags, wraps orreusable containers) do the best job of (1) keeping food fresh for “thelong haul”, (2) at lowest overall cost, and (3) with minimum adverseenvironmental impact. It “top rates” ZIPLOC® Pleated Freezer Bags (atpage 145). It points out that food stored in plastic containers cansuffer from freezer burn if the container contains too much air.Concerning “wraps” (plastic films and freezer papers) it advised againstdouble wrapping because of cost and environmental reasons and “our testsshowed that double wrapping doesn't afford much extra protectionanyway”. Nowhere does the article disclose or suggest the inventiondescribed hereinafter.

The patent literature contains descriptions of various types of bagshaving liners or double walls including some space between the walls.Some of these patents relate to the transportation and storage of food.U.S. Pat. No. 4,211,091 (Campbell) concerns an “Insulated Lunch Bag”.U.S. Pat. No. 4,211,267 (Skovgaard) describes a “Carrying Bag” for“getting home with frozen food before it thaws”. U.S. Pat. No. 4,797,010(assigned to Nabisco Brands) discloses a duplex paper bag as a“reheatable, resealable package for fried food”. U.S. Pat. No. 4,358,466(assigned to The Dow Chemical Company) relates to an improved “FreezerTo Microwave Oven Bag”. The bag is formed of two wing shaped pouches oneach side of an upright spout. U.S. Pat. No. 5,005,679 (Hjelle) concerns“Tote Bags Equipped With A Cooling Chamber”. All of these food bagsappear to have very thick food contacting walls compared to theinvention described hereinafter. None of these patents appear to focuson freezer burn.

Books on “Home Freezing” are of interest to this invention. Concerning“Wrapping Meat for the Freezer”, the book “Rodale's Complete Book ofHome Freezing” by Marilyn Hodges and the Rodale Test Kitchen staff(1984) suggested the inconvenient method of wrapping meat chunks in asingle layer of freezer paper and “sucking out the air with a straw”(trying to avoid getting blood into ones mouth) in order to reduce theamount of dehydration in the freezer (see page 173).

There is clearly still a great need to improve existing methods ofpackaging fresh meat, as determined by consumer surveys, coupled withthe fact that there is a 45 billion dollar retail market in the U.S.alone, consuming about 225 million dollars worth of plastic packagingmaterials annually.

SUMMARY OF THE INVENTION

In contrast to the known prior art, it has now been surprisinglydiscovered that certain types of multiple walled plastic bags (definedherein as “multibags”) are better than corresponding single wall freezerbags (having equal or greater weight than the multiple walled bags) foruse as a functional freezer bag for preserving red meat without freezerburn. All of the independent claims hereinafter concern different butrelated broad aspects of the invention, and are hereby incorporated byreference.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a front elevational view of a prior art reclosablethermoplastic single wall bag having a zipper.

FIG. 1B is a cross-sectional view taken along reference line 1B—1B ofFIG. 1A.

FIG. 2A is a front elevational view of a double wall bag in accordancewith the present invention, (i) having a thin inner wall or liner, and(ii) having “common side seals” between the inner and outer walls and,optionally, (iii) a vent through the outer wall to connect the spacebetween the inner and outer walls to the atmosphere outside the outerwall; and mouth seal that is optionally a blanket heat seal.

FIG. 2B is a partial cross-sectional view taken along line 2B—2B of FIG.2A.

FIG. 2C is a partial cross-sectional view taken along line 2C—2C of FIG.2A.

FIG. 3A is a front elevational view of another double wall bag of thepresent invention, with “separate side seals”.

FIG. 3B is a partial cross-sectional view taken along line 3B—3B of FIG.3A.

FIG. 3C is a cross-sectional view taken along line 3C—3C of FIG. 3B.

FIG. 4A is a front elevational view of a further double wall bag of thepresent invention, with the space between the inner and outer wallsconnected with the space within the inner bag.

FIG. 4B is a partial cross-sectional view taken along line 4B—4B of FIG.4A.

FIG. 4C is a partial cross-sectional view taken along line 4C—4C of FIG.4B.

FIG. 5A is also a front elevational view of a double wall bag of thepresent invention, with the space between the inner and outer wallsconnected to the space within the inner bag.

FIG. 5B is a partial cross-sectional view along line 5B—5B of FIG. 5A.

FIG. 5C is a partial cross-sectional view along line 5C—5C of FIG. 5A.

FIG. 6A is a front elevational view of a package of “meat in a closedbag” of the invention.

FIG. 6B is a cross-sectional view taken along reference line 6B—6B ofFIG. 6A.

FIG. 7 is a diagrammatic flow diagram for one manual process of thepresent invention for making experimental freezer bags.

FIG. 8 is a diagrammatic flow diagram for a process of the presentinvention for making freezer bags (with a common edge seal between theliner bag and support bag).

FIG. 9A is a front elevational view of a double wall bag in accordancewith the present invention, having a liner bag prepared from textured,particularly embossed film on at least the inside surface 11S.

FIG. 9B is a cross-sectional view taken along reference line 9B—9B ofFIG. 9A.

FIG. 10 is an isometric view of one process for preparing mouth sealsthat are extruded blanket seals.

DETAILED DESCRIPTION OF THE INVENTION

According to a first aspect of the invention, there is provided afreezer bag comprising a multibag of at least two bags, the first bagbeing the innermost, that is, (hereinafter “liner”), the second bag(hereinafter “support”) surrounding the liner, the support bag having amouth and a throat, and the liner bag having a mouth, and a mouth-sealconnecting the liner's mouth to the support's throat, characterized inthat:

the liner is thermoplastic and has a thickness (t) of less than 2.0 mil(50 micron).

According to a second aspect, there is provided a multi bag of at leasttwo bags, the first bag being both thermoplastic and the innermost bag(hereinafter “liner”) the second bag (hereinafter “support”) surroundingthe liner, the support bag having a mouth and a throat, and the linerbag having a mouth, and a mouth-seal connecting the liner's mouth to thesupport's throat characterized in that:

the mouth-seal is a blanket heat seal.

In a third aspect, the present invention provides a multibag of at leasttwo bags, the first bag being the inner most (hereafter “liner”), thesecond bag (hereinafter “support”) surrounding the liner and, thesupport bag having a mouth and a throat, and the liner bag having amouth, and a mouth-seal connecting the liner's mouth to the support'sthroat, characterized in that the liner is textured.

The present invention also provides thermoplastic nonhalogenated filmfor use as meat-contacting packaging material, characterized by thecombination:

(i) the film has a thickness (t) of less than 2 mil (50 μm);

(ii) the film has a Transverse Direction 2 percent Secant Modulus (TDSM)of less than 40,000 psi/100 percent extension (1.86×10⁸ Pa/100 percentextension) when determined in accordance with ASTM D 882-83 (StandardTest methods for Tensile Properties of Thin Plastic Sheeting), Method Awith a jaw gap of 4 inches (10 cm) for test specimens having an initialwidth of 1 inch (2.5 cm), except that the Initial Strain Rate is 0.25inches per inch per minute (0.25 cm per cm per minute) with a crossheadspeed of 1 inch (2.5 cm) per minute;

(iii) the film has a calculated value, Z-value of less than 20,000 mil³psi (2.25 mm³·kPa)/100 percent extension wherein Z-value equals(t³)×(TDSM);

(iv) at least one surface of the film has a contact angle in a range offrom 65° to 75° at room temperature (20° C.) relative to raw beef meatjuice, as determined by Advancing Contact Angle Determination with aContact Goniometer (A-100 Ráme-Hart); and

(v) the film is an embossed film.

Further, the invention provides a process for preparing reclosablethermoplastic bags by the steps of (a) forwarding a first thermoplasticfilm having a thickness greater than 1 mil (25 μm) and having mateablemale and female closure elements along opposed edges of thethermoplastic film; (b) folding the film and mating the male and femaleclosure elements; (c) seal cutting to length in the machine direction toform bags, and stacking and packing the bags, characterized by theadditional steps of:

(d) In parallel with step (a), forwarding a sheet of thermoplastic filmhaving a thickness (t) of less than 2 mil (50 μm);

(e) Prior to step (b) overlaying and aligning the second thermoplasticfilm onto the first thermoplastic film between the male and femaleclosure elements;

(f) Still prior to step (b), heat-sealing the second thermoplastic filmto the first thermoplastic film at two locations, adjacent to andbetween the male and female closure elements; and,

(g) In step (c), seal cutting to form a common edge seal between theliner bag and support bag.

The invention also provides aged frozen freezer bagged beef having afrozen age of at least 6 months and having metmyoglobin (MMb) at thebeef's surface; characterized in that:

The amount of MMb at the surface of the beef is less than 60 percent ofthe total myoglobin content as determined by a conventional absorptionspectrophotometry test.

Certain terms used in this specification are hereby defined as follows:

“Multiwall (noun)” is a “multiwall bag” (in accordance with Webster's“complete” dictionary at page 1486);

“Multiwall (adjective)” is “having a wall made-up of several layers” (inaccordance with Websters “complete” dictionary at page 1486).

A “double bag” is two bags, one within the other, which double bag canbe separated into two separate bags, which separate bags can then reformthe double bag (as for bagging groceries at a supermarket).

A “duplex bag” is hereby defined as an integral bag consisting of anouter support bag and an inner liner bag, wherein the liner bag ispartly (but not completely) joined to the support bag.

A “multi bag” is hereby defined as an integral bag having at least anouter support bag and an inner liner bag, wherein the liner bag ispartly (but not completely) joined to the support bag; and optionallyadditional layers between the liner bag and the support bag. Thesimplest form of a multibag is a duplex bag. The term “multibag” doesnot appear in Webster's Dictionary.

The liner bag of the freezer bag of the invention preferably has aTransverse Direction 2 percent Secant Modulus (TDSM) of less than 40,000(preferably less than 27,000) psi/100 percent extension (1.86×10⁸ Pa/100percent extension) when determined in accordance with ASTM D 882-83(Standard Test Methods for Tensile Properties of Thin Plastic Sheeting),Method A with a jaw gap of 4 inches (10 cm) for test specimens having aninitial width of 1 inch (2.5 cm), except that the Initial Strain Rate is0.25 inches per inch per minute (0.25 cm per cm per minute) with acrosshead speed of 1 inch (2.5 cm) per minute. When TDSM has a valueless than 27,000 units, such products are typically prepared byso-called well known cast-film processes. When TDSM has a value in arange of 27,000 to 40,000 units, such products are typically prepared bywell know blown-film proesses. Such liners suitably comprisesthermoplastic film having a calculated value, Z-value, of less than60,000 mil³ psi (6.75 mm³ kPa)/100 percent extension wherein Z-valueequals (t³)×(TDSM). Preferably, the liner's Z-value is less than 20,000mil³ psi (2.25 mm³·kPa)/100 percent extension; especially in a rangefrom 2,000 to 10,000 mil³ psi (0.2 to 1.1 mm³·kPa); and most preferablyin a range from 3,000 to 6,000.

Suitably the thermoplastic film comprises homopolymers and copolymers ofethylene having a specific gravity of less than 0.930 gm/cc.

In a preferred embodiment, the multibag consists of 2 bags and whereinthe support has a Z-value in a range of 50,000 to 150,000 mil³ psi (5.6to 16.9 mm³·kPa)/100 percent extension.

Thickness of films (t and T) are easily determined by conventionalspacing loaded thickness gauges.

Advantageously, the liner's food contactable surface has a contact anglein an amount from 65° to 75° at room temperature (20° C.) relative toraw beef meat juice, as determined by Advancing Contact AngleDetermination with a Contact Goniometer (A-100 Ráme-Hart). The liner'sfood contactable surface suitably has been corona-treated. Usually, theliner's thickness (t) will be in a range of 0.3 to 1.0 mil (8 to 25 μm);preferably 0.5 to 0.7 mil (12 to 18 μm) and the support bag's thickness(T) will be in a range from 1.0 to 4.0 mil (25 to 100 μm); preferablyfrom 1.3 to 3.0 mil (35 to 75 μm); and more preferably from 1.5 to 2.0mil (40 to 50 μm). However, other thickness can be used.

Suitably, the support bag is thermoplastic.

Usually, the freezer bag will have a liquid storage capacity in a rangeof 1 pint to 2 gallons. The space between the liner bag and the supportbag can be vented to atmosphere outside the support; essentiallyunvented and containing constant mass of material; or vented to thespace within the liner bag. In the latter option, the seal between thesupport bag's throat and the liner bag's mouth suitably is discontinuousand the space between the liner and the support comprises hygroscopicmaterial. Preferably, the hygroscopic material is selected fromhydroxypropyl methylcellulose and polyvinyl alcohol. The liner bag canbe connected to the support bag by common edge seats or the liner bagsedge seals can be separate from the support-bags's edge seals.

The support bag may comprise mateable male and female closure elementsalong opposed inner surfaces of the support bag. The liner bag can havea color or texture that is different from the color or texture of atleast part of the support bag. It is particularly preferred that theliner bag is textured, for example, embossed. It has been found thatliner film having an embossed surface has greater cling to raw red meatas determined by a static coefficient of friction test analogous to thatdescribed in ASTM D 1894-87. When the liner bag is textured the upperthickness limitation of the first embodiment is not applicable.Thicknesses of up to 3.0 mil may be used when the liner's film isembossed.

Preferably, the connection between the liner bag and the support bag issuch that the liner can be stroked to conform to the external geometryof a ribeye steak placed within the liner bag.

The multibags can have more than two layers. For example, it can havethree layers and in this embodiment it is preferred that the third layeris located between the liner bag and the support bag and causes theliner bag to be conformable to the outside geometry of food within theliner bag while food in the bag is being frozen. Suitably, the liner'sthickness (t) is in a range from 1.0 to 2.0 mil (25 to 50 μm), and thethird bag is formed of elastic fabric.

It is preferred that the support bag is sealed to the liner bag by a“mouth seal” that is a “blanket heat seal,” preferably an “extruded heatseal.” By “extruded blanket seal”, we mean a blanket seal that isextruded directly onto the overlapped liner film and support film.However, the mouth-seal can also be made by using (i) conventional hotmelt adhesion between the liner and the support; or (2) conventional hotpress sealing; or even some form of solvent sealing.

EXAMPLES OF THE INVENTION

The experimental work that led to the aspects of the invention claimedhereinafter involved time-consuming hand fabrication of numerousdifferent types of “multibag” defined above; repackaging of meat in themultibags; and evaluation of the performance of the multibags relativeto each other and other controls being commercially available freezerbags, during and after many months of storage in a freezer.

The experimental work involved the sequential evaluation of three maintypes of prototype, types A, B, and C described below.

Type-A Prototypes

Type-A prototypes were all three-layer multibags made essentially inaccordance with FIGS. 5A, 5B and 5C having a support bag (12), a linerbag (11), a third layer (77), and vent holes (11 c) for venting thespace between the liner bag and the support bag to the space within theliner bag.

More specifically, Type-A1 multi bags were fabricated as follows:

a. A support bag (12) being an outer layer of polyethylene film (usedfor making ZIPLOC® storage bag 1.75 mil (45 μm);

b. A liner bag (11) being an inner layer of polyethylene film 1.75 mil(45 μm) thick with 800 microholes (11 c) having hole diameters of 10 μmas vent holes to permit moisture to move freely into and out of themiddle layer; and

c. A third layer (77) being a hygroscopic film having a thickness of 1.5mil (38 μm) and moisture content of around 10 percent by weight(METHOCEL® cellulose ethers film made by Polymer Films, Inc.-Rockville,Conn.). METHOCEL® is a registered Trademark of The Dow Chemical Company.More specifically, typical properties of the film are found in the June,1986 data sheet of Polymer Films Inc., for the product named “EM IIDOWater Soluble Film”. The product was identified as having the primaryconstituent being Hydroxypropyl Methyl Cellulose Resin having CAS No of009004-65-3.

Further, it will be noted from FIG. 5A that the edge seals AD and BC ofthe support bag (12) are essentially “common” with the edge seals ad andbc of the liner bag (11).

Type-B Prototypes

Type-B prototypes were all three-layer multibags essentially similar tothe Type-A prototypes except that the liner bag (11) had a thickness of1.2 mil (30 μm) (instead of 1.75 mil (45 μm)); and except the liner (11)had no microholes therein and that the space between the liner bag andthe support bag was essentially completely unvented.

Type-C Prototypes

Type-C prototypes were all multibags of the duplex variety as shown inFIGS. 2A, 2B, 2C, 3A, 3B, 3C, 4A, 4B and 4C and having a support bag(12) having a thickness of 1.75 mil (45 μm) and a liner bag (11) havinga thickness of 0.6 mil (15 μm) without any “third layer or wall” betweenthe liner bag and the support bag. The mouth seal AB between the liner'smouth and the support's throat was a hot press seal rather than theblanket seal 55 shown in FIGS. 2A, 2B and 3A and 3B.

The Type-C multibags were given a secondary classification (denoted bythe letter “C” or the letter “S” dependent upon whether the bags had“common edge seals” or “separate edge seals”. The liner's edge seals areshown on the lines ad and bc in FIGS. 2A, 3A and 4A. The edge seals ofthe support bag (12) are shown by the lines AD and BC in FIGS. 2A, 3Aand 4A. Clearly, in FIG. 2A the edge seals are essentially “common”;whereas in FIGS. 3A and 4A the edge seals are “separate”.

The bags were fabricated by hand. FIG. 7 is a diagrammatic flow diagramfor making Type-CC multi bags.

The Type-C multibags were given a tertiary classification (1, 2, or 3)according to whether the space between the support bag (12) and theliner bag (11) was (1) vented to the space within the liner bag (asshown in FIG. 4C); or (2) not vented (as shown in FIGS. 3A, 3B and 3C);or (3) vented to the surrounding atmosphere (as shown by the vent (99)in dotted line in FIGS. 2A and 2B).

The Type-C multibags could be given a fourth clarification dependentupon whether the “mouth seal” is merely a “simple hot press seal”(hereinafter SHPS) “not simple hot press seal” (hereinafter NSHPS).

Examples of NSHPS include both “hot melt adhesion” and “blanket heatseal” (hereinafter BHS) particularly wherein a blanket strip is extrudedonto both the inner mouth of the liner and the inner throat of thesupport (hereinafter EBHS). One possible EBHS process is illustrated inFIG. 10. EBHS permits high speed.

Evaluation Procedure

All prototype multibags were essentially evaluated relative to controlbags in the following way by actually using the bags as potentialfreezer bags containing boneless beef steak.

1. Beefsteak samples were initially weighed before packing in the bags.Each bag had one beef steak. The bags were placed in a commercialfreezer with a set point of 0° F. (−18° C.).

2. The freezer was occasionally opened and closed for the purpose ofobserving the samples.

3. Physical observation (including bags conformation around steaks,formation of ice crystals, visible dry spots, and discoloration) weremade daily during the first two weeks and then once every week for thenext eight months for prototypes Type-A and Type-B. Type-C wasphysically observed over a period of three months. Frozen beef steakswere photographed in color both inside and outside the bags, then thawedand photographed again.

4. Percent weight loss and the amount of drips were measured on thethawed steaks. Amount of drips is defined as the blood-like fluidexuding from frozen meat upon thawing.

5. “Unexpected effects” were noted as appropriate.

Short Term Results—Types A, B and C

Various Type-A prototypes and Type-B prototypes were evaluatedsimultaneously, and sequentially in a staggered manner.

Type-A1 described above was evaluated because the film was hygroscopicand in the hope that it might help to prevent moisture escaping from themeat during storage in the freezer.

However, an unexpected result occurred almost immediately. In particularit was discovered that, with a hygroscopic film layer between the linerbag and the support bag, the hygroscopic layer and the liner bag changedshape very rapidly and “conformed” to the shape of the beef steak. Inother words it was highly beneficial in excluding air from the spacearound the beef steak.

It came as a second major surprise when the Type-B multibag also tightlyconformed the liner bag around the steak as a short-term phenomenon.

The apparent success of the Type-B multi bag led to the design of theType-C multi bag. Two types of Type-C bags were evaluated: Type-CC2 andType-CS2. Again a surprisingly result occurred. The Type-CC2 multibagappears to conform more easily to the shape of the beef steak atpackaging and “before” the beef steak package is placed in the freezeras shown in FIG. 6A. With hindsight, it is possible to make variousspeculations based upon the fact that the unvented bag essentially hasconstant mass of air between the liner bag and the support bag.

Long-Term Results—Types A and B

Beef steaks in regular freezer bags (control) developed many large icecrystals and severe discoloration (bright red color faded into faintbrown). Severe freezer burn, as evidenced by large discolored dry spots,was observed on the steak in both frozen and thawed states.

Beef steaks in the Type-A three-layer multibags (with a perforated innerlayer) were in excellent condition. Formation of ice crystals wassignificantly reduced, the bright red color was maintained and nodiscoloration was observed. No freezer burn on the surface of the steakswas observed.

The Type-B three-layer multibags with nonperforated film as the innerlayer showed similar results to those obtained with Type-A multi bags.

A key hindsight observation that may explain the significant differencein quality performance between the control bags and the three-layer bagsis that the middle and inner layers of the three-layer bags had tightlyconformed around the steak which resulted in reducing air pockets andsubsequent formation of ice crystals.

A comparison of weight loss and amount of drips between treatmentsshowed that weight loss of the steaks correlated well with the amount offormation of ice crystals. Beef steaks stored in regular freezer bagshad a severe weight loss (up to 20.5 percent) in eight months and theamount of drips was 2.06 percent. Beef steaks stored in the three-layerbags (with a perforated inner layer) had a significantly less weightloss (4.3 percent) than the control and the amount of drips was 1.93percent. The least amount of weight loss (1.9 percent) and drips (0.26percent) was measured with steaks stored in the three-layer bags (withnonperforated inner layer). The difference in performance between thethree-layer bags and control bags relate to the ability of thethree-layer bags to conform tightly around the meat, which led tominimizing air pockets. As a result of conforming, the dehydrationprocess, that leads to freezer burn, was reduced significantly.

It was concluded that the quality of frozen beef steaks, stored in theType-A and Type-B three-layer multibags was superior compared to regularfreezer storage bags (control). The freezer burn was minimizedsignificantly due to the conforming of the inner and middle layers ofthe three-layer bags onto the beef steaks.

Long-Term Results—Type-C

The Type-CC2 and Type-CS2 multibags also performed significantly betterthan the commercially available freezer bags used as control. Theirsuperior performance can be attributed, with the benefit of hindsight,to the tendency of the liner bag to “conform” to the food and minimizethe headspace available for ice formation. It should perhaps be notedthat performance advantages of these prototypes were less significant intests with irregularly shaped food such as broccoli and chicken withbones.

Various properties of the Type-C liner bag and support bag were measuredand compared with the corresponding properties of the commerciallyavailable freezer bags. For example, Relative Stiffness, as determinedby the DowBrands Relative Flexural Stiffness in the Transverse Directionof the Type-C liner was 1 to 2 orders of magnitude lower thancommercially available “freezer bags” (for example, 5,300 psi cubic milscompared with 304,000 psi cubic mils) (34 kPa/mm³).

What is claimed is:
 1. A recloseable multibag freezer bag comprising: aninner liner bag defining an inner wall of the multibag, the liner baghaving a mouth through which an interior of the liner bag is accessible,the liner bag being formed of a thermoplastic film having a thickness tof less than 2.0 mil and having a Transverse Direction two percentSecant Modulus (TDSM) of less than 40,000 psi/100 percent extension whendetermined in accordance with ASTM D 882-83 (Standard Test methods forTensile Properties of Thin Plastic Sheeting), Method A with a jaw gap of4 inches for test specimens having an initial width of 1 inch, exceptthat the Initial Strain Rate is 0.25 inches per inch per minute with acrosshead speed of 1 inch per minute; an outer support bag surroundingthe liner bag and defining an outer wall of the multibag, the supportbag being formed of a thermoplastic film, and having a mouth and athroat, the liner bag mouth being joined by a mouth seal to the throatof the support bag along the entire length of the liner bag mouth toform a substantially enclosed air space between the liner bag and thesupport bag; and a recloseable mouth seal affixed to the mouth of thesupport bag to provide recloseable access to the interior of the linerbag through the mouth of the support bag while maintaining the enclosedair space between the liner and support bags.
 2. The freezer bagaccording to claim 1, wherein the film of the liner bag is formed of amaterial selected from the group consisting of homopolymers andcopolymers of ethylene having a specific gravity of less than 0.930gm/cm³.
 3. The freezer bag according to claim 1, wherein the film of thesupport bag has a thickness T in a range from 1.0 to 4.0 mil.
 4. Thefreezer bag according to claim 1, wherein the liner bag and at leastpart of the support bag differ from one another in at least one of colorand texture.
 5. The freezer bag according to claim 1, wherein the filmof the liner bag has been corona-treated.
 6. The freezer bag accordingto claim 1, wherein the recloseable mouth seal comprises recloseableclosure elements disposed along opposed inner surfaces of the supportbag.
 7. The freezer bag according to claim 1, wherein the thickness t ofthe liner bag film is in a range from 0.3 to 1.0 mil.
 8. The multibag ofclaim 1, wherein the liner bag is textured.
 9. The freezer bag accordingto claim 1, wherein the mouth-seal is selected from a hot melt adhesionseal and a blanket heat seal.
 10. The freezer bag according to claim 1,wherein the TDSM of the film of the liner bag is less than 27,000psi/100 percent extension.
 11. The freezer bag according to claim 1,wherein the enclosed air space between the liner bag and the support bagis vented to atmosphere outside the support bag.
 12. The freezer bagaccording to claim 1, wherein the enclosed air space between the linerbag and the support bag is essentially unvented.
 13. The freezer bagaccording to claim 1, wherein the enclosed air space between the linerbag and the support bag is vented to the interior of the liner bag. 14.The freezer bag according to claim 13, further comprising a hygroscopicmaterial selected from hydroxypropyl methylcellulose and polyvinylalcohol disposed within the enclosed air space between the liner bag andthe support bag.
 15. The freezer bag according to claim 1, furthercomprising an intermediate layer, located between the liner bag and thesupport bag, precipitating the liner bag to be conformable to theoutside geometry of food within the liner bag while the food is beingfrozen.
 16. The freezer bag according to claim 1, wherein the film ofthe liner bag has a calculated value, Z-value, which equals (t³)×(TDSM),of less than 60,000 mil³ psi/100 percent extension.
 17. The freezer bagaccording to claim 16, wherein the calculated value, Z-value of the filmof the liner bag is less than 20,000 mil³ psi/100 percent extension. 18.The freezer bag according to claim 16, wherein the calculated value,Z-value of the film of the liner bag is in a range between 2,000 and10,000 mil³ psi/100 percent extension.
 19. The freezer bag according toclaim 16, wherein the calculated value, Z-value of the film of the linerbag is in a range between 3,000 and 6,000 mil³ psi/100 percentextension.
 20. A recloseable multibag freezer bag comprising: an innerliner bag defining an inner wall of the multibag, the liner bag beingformed of a thermoplastic film having (i) a thickness t, (ii) aTransverse Direction two percent Secant Modulus TDSM determined inaccordance with ASTM D 882-83 (Standard Test methods for TensileProperties of Thin Plastic Sheeting), Method A with a jaw gap of 4inches for test specimens having an initial width of 1 inch, except thatthe Initial Strain Rate is 0.25 inches per inch per minute with acrosshead speed of 1 inch per minute, and (iii) a calculated value,Z-value, which equals (t³)×(TDSM), of less than 60,000 mil³ psi/100percent extension, the liner bag having a mouth through which aninterior of the liner bag is accessible; an outer support bagsurrounding the liner bag and defining an outer wall of the multibag,the support bag being formed of a thermoplastic film and having a mouthand a throat, the liner bag mouth being joined by a mouth seal to thethroat of the support bag along the entire length of the liner bag mouthto form a substantially enclosed air space between the liner bag and thesupport bag; and a recloseable mouth seal affixed to the mouth of thesupport bag to provide recloseable access to the interior of the linerbag through the mouth of the support bag while maintaining the enclosedair space between the liner and support bags.
 21. The freezer bagaccording to claim 20, wherein the film of the liner bag is formed of amaterial selected from the group consisting of homopolymers andcopolymers of ethylene having a specific gravity of less than 0.930gm/cm³.
 22. The freezer bag according to claim 20, wherein the film ofthe support bag has a thickness T in a range from 1.0 to 4.0 mil. 23.The freezer bag according to claim 20, wherein the liner bag and atleast part of the support bag differ from one another in at least one ofcolor and texture.
 24. The freezer bag according to claim 20, whereinthe liner bag has been corona-treated.
 25. The freezer bag according toclaim 20, wherein the recloseable mouth seal comprises recloseableclosure elements disposed along opposed inner surfaces of the supportbag.
 26. The freezer bag according to claim 20, wherein the thickness tof the liner bag film is in a range from 0.3 to 1.0 mil.
 27. Themultibag of claim 20, wherein the liner bag is textured.
 28. The freezerbag according to claim 20, wherein the mouth-seal is selected from a hotmelt adhesion seal and a blanket heat seal.
 29. The multibag of claim20, wherein the film of the liner bag is embossed, and the thickness tof the film of the liner bag is in a range of from 0.5 to 3.0 mil. 30.The freezer bag according to claim 20, wherein the calculated value,Z-value of the film of the liner bag is less than 20,000 mil³ psi/100percent extension.
 31. The freezer bag according to claim 20, whereinthe calculated value, Z-value of the film of the liner bag is in a rangebetween 2,000 and 10,000 mil³ psi/100 percent extension.
 32. The freezerbag according to claim 20, wherein the calculated value, Z-value of thefilm of the liner bag is in a range between 3,000 and 6,000 mil³ psi/100percent extension.
 33. The freezer bag according to claim 20, whereinthe enclosed air space between the liner bag and the support bag isvented to atmosphere outside the support bag.
 34. The freezer bagaccording to claim 20, wherein the enclosed air space between the linerbag and the support bag is essentially unvented.
 35. The freezer bagaccording to claim 20, wherein the enclosed air space between the linerbag and the support bag is vented to the interior of the liner bag. 36.The freezer bag according to claim 35, further comprising a hygroscopicmaterial selected from hydroxypropyl methylcellulose and polyvinylalcohol disposed within the enclosed air space between the liner bag andthe support bag.
 37. The freezer bag according to claim 20, furthercomprising an intermediate layer, located between the liner bag and thesupport bag, precipitating the liner bag to be conformable to theoutside geometry of food within the liner bag while the food is beingfrozen.